In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductor wafers, the ion implantation system injects a selected ion species into the wafer to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n-type extrinsic material wafers, and implanting materials such as boron, gallium or indium creates p-type extrinsic material portions in a semiconductor wafer.
FIG. 1 illustrates a conventional ion implantation system 10 having a terminal 12, a beamline assembly 14, and an end station 16. The terminal 12 includes an ion source 20 powered by a high voltage power supply 22 that produces and directs an ion beam 24 to the beamline assembly 14. The beamline assembly 14 consists of a beamguide 32 and a mass analyzer 26 in which a dipole magnetic field is established to pass only ions of appropriate charge-to-mass ratio through a resolving aperture 34 at an exit end of the beamguide 32 to a workpiece 30 (e.g., a semiconductor wafer, display panel, etc.) in the end station 16. The ion source 20 generates charged ions that are extracted from the source 20 and formed into the ion beam 24, which is directed along a beam path in the beamline assembly 14 to the end station 16. The ion implantation system 10 may include beam forming and shaping structures extending between the ion source 20 and the end station 16, which maintain the ion beam 24 and bound an elongated interior cavity or passageway through which the beam 24 is transported to one or more workpieces 30 supported in the end station 16. The ion beam transport passageway is typically evacuated to reduce the probability of ions being deflected from the beam path through collisions with air molecules.
Low energy implanters are typically designed to provide ion beams of a few hundred electron volts (eV) up to around 80–100 keV, whereas high energy implanters can employ linear acceleration (linac) apparatus (not shown) between the mass analyzer 26 and the end station 16, so as to accelerate the mass analyzed beam 24 to higher energies, typically several hundred keV, wherein DC acceleration is also possible. High energy ion implantation is commonly employed for deeper implants in the workpiece 30. Conversely, high current, low energy ion beams 24 are typically employed for high dose, shallow depth ion implantation, in which case the lower energy of the ions commonly causes difficulties in maintaining convergence of the ion beam 24. Different forms of end stations 16 are found in conventional implanters. “Batch” type end stations can simultaneously support multiple workpieces 30 on a rotating support structure, with the workpieces 30 being rotated through the path of the ion beam until all the workpieces 30 are completely implanted. A “serial” type end station, on the other hand, supports a single workpiece 30 along the beam path for implantation, whereby multiple workpieces 30 are implanted one at a time in serial fashion, with each workpiece 30 being completely implanted before implantation of the next workpiece 30 begins.
The implantation system 10 of FIG. 1 includes a serial end station 16, wherein the beamline assembly 14 includes a lateral beam scanner 36 that receives the ion beam 24 having a relatively narrow profile (e.g., a “pencil” beam), and scans the beam 24 back and forth in the X-direction (e.g., along a lateral scan direction in a horizontal scan plane) to spread the beam 24 out into an elongated “ribbon” profile (e.g., referred to as a scanned beam or a ribbon beam) having an effective X-direction width that is at least as wide as the workpiece 30. The ribbon beam 24 is then passed through a parallelizer or collimator 38 that directs the ribbon beam generally parallel to the Z-direction toward the workpiece 30 (e.g., the parallelized beam 24 is generally normal to the workpiece surface for non-angled implants). A final energy adjustment system 39 is located between the parallelizer 38 and the location of the workpiece 30, which operates to accelerate or decelerate the scanned and parallelized (e.g., collimated) beam 24. The workpiece 30 is mechanically translated in another orthogonal direction (e.g., a “Y” direction in and out of the page in FIG. 1), wherein a mechanical actuation apparatus (not shown) translates the workpiece 30 in the Y-direction during X-direction beam scanning by the beam scanner 36, whereby the beam 24 is imparted on the entire exposed surface of the workpiece 30. The X-direction beam scanning is commonly referred to as a “fast scan”, whereas the mechanical translation of the workpiece 30 along the Y-direction is referred to as a “slow scan”.
In the manufacture of integrated circuit devices and other products, it is desirable to uniformly implant the dopant species across the entire workpiece 30. As the ion beam 24 is transported along the beam path toward the workpiece 30, the beam 24 encounters various electric and/or magnetic fields and devices that may alter the beam dimensions and/or the integrity of the beam 24, leading to non-uniformity of dopants in the implanted workpiece 30. Absent countermeasures, space charge effects, including mutual repulsion of positively charged beam ions, tend to diverge the beam 24 (e.g., possibly leading to beam “blowup”). Low energy ion beams 24 are particularly susceptible to beam divergence or beam blowup when transported over long distances. Furthermore, where the final energy adjustment system 39 is operated so as to decelerate the ions of the beam 24, the space charge effects are more pronounced in the deceleration gap between the collimator 38 and the workpiece 30. Accordingly, it is desirable to focus the scanned ion beam 24 after collimation to counteract the heightened mutual repulsion of the decelerated beam 24.